JP2861871B2 - Control method of winding temperature of hot rolled steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to hot rolled high Si
The present invention relates to a method for controlling a winding temperature of a hot-rolled steel sheet for cooling a steel sheet to a desired winding temperature on a run-out table.

[0002]

2. Description of the Related Art A hot-rolled steel sheet is cooled to a predetermined temperature on a run-out table and then wound around a coiler. Controlling the winding temperature on the run-out table is an important step in determining the mechanical properties of the steel sheet. Therefore, the amount of water injected from the cooling headers disposed above and below the run-out table surface is determined so as to obtain predetermined mechanical properties.

FIG. 1 is a schematic diagram showing an outline of winding temperature control on a run-out table. The steel sheet 1 coming out of the finishing mill 2 is cooled on the run-out table 3 by pouring water from the cooling headers 4, 5 and wound around the coiler 6. At this time, the temperature of the steel sheet before cooling is measured by the thermometer 7, and the temperature of the steel sheet after cooling is measured by the thermometer 8, respectively. The controller 9 is basically a feedforward controller, which predicts and calculates the temperature after cooling (winding temperature) and determines the amount of water to be injected from the cooling headers 4 and 5 so that the calculated value matches the target value. I do.

[0004] By the way, in the production of high-tensile steel sheets,
Winding temperature of 400 to 550 depending on required strength
Set to relatively low temperature. However, in the region where the temperature of the steel sheet is low, the boiling phenomenon is in a transition boiling state in which the film transitions from film boiling to nucleate boiling, and the steel sheet temperature greatly changes by opening and closing a valve. FIG. 2 shows the relationship between the heat transfer coefficient ratio and the steel sheet surface temperature when the steel sheet surface temperature is 600 ° C. Transition boiling at a temperature lower than 500 ° C,
In this state, the heat transfer coefficient ratio sharply increases as the steel sheet surface temperature decreases, so that cooling becomes unstable.

In order to solve this problem, Japanese Patent Publication No. Hei 6-2
No. 48 proposes to cool the steel sheet in a stable state by injecting water from the upper and lower cooling headers in the high temperature area where the cooling water is film boiling, and by injecting only the lower surface of the steel sheet in the transition boiling area. Have been.

[0006]

In controlling the winding temperature of a hot-rolled steel sheet as shown in FIG. 1, the steel sheet surface temperature measured at the exit side of the finishing mill 2, the steel sheet speed, and the upper and lower cooling headers 4 and 5 are used. , And the temperature of the steel sheet after cooling (winding temperature) is calculated based on the water injection amount, the water heat transfer coefficient curve shown in FIG. Then, the water injection amount is determined so that the calculated temperature becomes the target temperature. Therefore, in order to accurately control the winding temperature to the target temperature, it is necessary to accurately predict and calculate the winding temperature.

When the Si content of a high-tensile steel sheet is relatively low, ie, less than 0.5%, the difference between the calculated value and the measured value of the steel sheet winding temperature is usually ± 20 ° C. or less. By using a technique such as feedback, accurate winding temperature control is performed. However, in the case of a high Si steel having a Si content of 0.5% or more, when the winding temperature is predicted and calculated using the same water-cooled surface heat transfer coefficient curve as that of the low Si steel, the difference between the calculated value and the predicted value is 100%. ° C or more, and even if feedback is used in combination, the control accuracy of the winding temperature is significantly reduced. This problem is due to the fact that the winding temperature cannot be accurately predicted and calculated.
However, even if the method proposed in Japanese Patent Application Laid-Open Publication No. H10-15064 is used, it cannot be solved at all.

[0008] An object of the present invention is to provide a method for controlling a winding temperature of a hot-rolled steel sheet which controls the winding temperature of a hot-rolled steel sheet made of high Si steel with high accuracy.

[0009]

According to the winding temperature control method of the present invention, when a hot-rolled steel sheet is water-cooled on a run-out table and wound, the winding temperature of the hot-rolled steel sheet is determined using a water-cooled surface heat transfer coefficient. In the winding temperature control of a hot-rolled steel sheet for controlling the water injection amount in the run-out table so that the calculated value matches the target value, the water-cooled surface of the high Si steel is The water cooling surface heat transfer coefficient is corrected so that the heat transfer coefficient is higher than the water cooling surface heat transfer coefficient of the low Si steel.

[0010]

In the high Si steel, as shown in FIG. 3, the oxide scale formed on the surface of the raw material remains after rolling, and as a result, the surface of the steel plate becomes rough. The present inventors have developed a high Si
The reason why the predicted calculated value of the winding temperature greatly deviated from the measured value by controlling the winding temperature of steel was determined by the difference in the cooling phenomenon due to the residual scale, and the following experiment was performed.

[0011] Table 1 shows the low Si steel and high S
For each of the i steels, a test piece having a plate thickness of 3.0 mm was prepared, each test piece was heated to 1220 ° C. for about 15 minutes, and then descaled, and water cooling was started from 800 ° C. to obtain a cooling curve. As a result, as shown in FIG. 4, it was found that the high Si steel had a cooling rate in the initial stage of cooling more than twice that of the low Si steel. Incidentally, the scale thickness after descaling is 21 to 22 μm for high Si steel and 6 to 14 μm for low Si steel.
μm.

Next, the heat transfer coefficient of the water-cooled surface of the high Si steel and the low Si steel was obtained by the back calculation based on the result of FIG. The results are shown in FIG. 5. In the region where the water cooling surface temperature is 350 ° C. or higher, the heat transfer coefficient of the high Si steel is larger than that of the low Si steel, and the difference Δh is particularly large in the region of 350 to 600 ° C. I understand.

[0013]

[Table 1]

In the winding temperature control method of the present invention, paying attention to this result, when the hot-rolled steel sheet is a high Si steel sheet, the water-cooled surface heat transfer coefficient is reduced in a region where the steel sheet temperature is 350 ° C. or more. It is made larger than in the case of cooling, and the prediction calculation error of the steel sheet temperature due to the difference in the amount of Si is made smaller. Thereby, the winding temperature is accurately predicted, and the winding temperature can be controlled with high accuracy.

The degree to which the heat transfer coefficient is increased is desirably set to the above-described heat transfer coefficient difference Δh, and is changed according to the water cooling surface temperature of the steel sheet.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the case where the winding temperature is controlled in a run-out table cooling facility having 14 cooling banks as shown in FIG.

In the run-out table cooling system shown in FIG. 6, the temperature of the steel sheet before cooling is measured by a thermometer 7 provided on the exit side of the finishing mill 2 and is provided between the No. 6 bank and the No. 7 bank. The temperature of the steel sheet during cooling is measured by the thermometer 10. The temperature of the steel sheet after cooling (winding temperature) is measured by a thermometer 8 provided on the inlet side of the coiler 6.
The controller 9 takes in the actual value of the rolling finish temperature from the thermometer 7 and takes in the actual value of the steel sheet speed from the finishing mill 2. The controller 9 performs the following processing using various actual values including these. The current temperature of the steel sheet 1 is calculated.
The steel plate temperature in each bank is predicted and calculated, and the valve opening / closing pattern of the upper and lower cooling headers is corrected so that each calculated value becomes the target value. In this way, the cooling process from the start of cooling to the end of cooling is feedforward controlled, and finally the winding temperature is controlled to its target value. If the actual value of the winding temperature taken in from the thermometer 8 does not match the target value, the amount of water injected from the upper and lower cooling headers is finely adjusted by feedback control depending on the deviation.

In the winding temperature control of the present embodiment, a technique for predicting and calculating the steel sheet temperature for each bank is important.
Equation 1 shows a heat transfer equation used when calculating the steel sheet temperature. Equation 2 shows the boundary condition of the steel sheet surface.

[0019]

(Equation 1)

[0020]

(Equation 2)

In equation (2), the heat velocities q _t and q _b on the upper and lower surfaces are given by equation (3).

[0022]

Equation 3] _{q t = q wt + q Rt} + q At q b = q Wb + q Rb + q Ab q Wt: water cooling of the heat flux q _Wb: water cooling of the heat flux q _Rt: radiation heat flux q _Rb: heat flux radiation q _At : heat flow rate of convection q _Ab : heat flow rate of convection

In equation (3), the heat flow rate of water cooling q _Wt ·
q _Wb is given by Equation 4 using the water-cooled heat transfer coefficient h _Wt · h _Wb [W / m ² ° C].

[0024]

Q _Wt = h _Wt (θ _S -θ _W ) q _Wb = h _Wb (θ _S -θ _W ) θ _S : Material surface temperature [° C] θ _W : Water temperature [° C]

The water-cooled heat transfer coefficient h _Wt · h _Wb is given by equation (5).

[0026]

(Upper surface) h _Wt = 1.163 × 10 ⁶ W ^0.425 (θ _S −θ _W ) ^-1 v ^-0.08 ｛1-0.02 (θ _S −40)｝ z (lower surface) h _Wb = 7.020 × 10 ⁵ W ^0.771 (θ _S −θ _W ) ⁻¹ ｛1−0.02 (θ _S −40)｝ z W: Water density [m ³ / m ² min] v: Steel sheet speed [m / min] z: Correction coefficient

Here, the heat transfer coefficient h _Wt · h _Wb of the upper and lower surfaces
Was determined, the correction coefficient z was as shown in Table 2. That is, when the hot-rolled steel sheet is a high Si steel,
In the upper and lower banks of No. 4, the correction coefficient z was made larger than in the case of low Si steel, and the heat transfer coefficients h _Wt and h _Wb of the upper surface and the lower surface were increased. The amount corresponds to the heat transfer coefficient difference Δh in FIG.

By performing such a correction of the heat transfer coefficient when the hot-rolled steel sheet is a high Si steel, the winding temperature can be accurately predicted and calculated, and the winding temperature can be controlled with high accuracy.

FIG. 7 shows the relationship between the calculated winding temperature and the measured value when the hot-rolled steel sheet is a high Si steel. In the case of the high Si steel, if the same hot rolling transfer coefficient as that of the low Si steel is used, the calculated temperature becomes 100 to 200 ° C. higher than the measurement temperature as indicated by ○. However, when the above-described correction of the heat transfer coefficient is performed, ◎
As shown in the figure, the difference between the calculated temperature and the measured temperature is several tens
Can be suppressed. This is a difference that can be eliminated by using feedback control together. The steel type at this time is shown in Table 1 and the plate thickness is 2.
6 to 2.9 mm.

[0030]

[Table 2]

[0031]

[Table 3]

In the above embodiment, the heat transfer coefficients h _Wt and h _Wb of the upper and lower surfaces were corrected when predicting and calculating the steel sheet temperature.
As shown in the above, when the steel sheet temperature is 600 ° C. or higher, the difference in heat transfer coefficient between the high Si steel and the low Si steel is relatively small,
At the lower surface of the steel plate, since the cooling is relatively stable without the remarkable boiling phenomenon due to the spray cooling as compared with the upper surface, the heat transfer coefficient h _Wt may be corrected only at the upper surface of the second half bank. Table 3 shows an example. Such approximate correction of the heat transfer coefficient is also effective in improving the calculation accuracy of the steel sheet temperature, and is included in the present invention.

[0033]

As described above, the method for controlling the winding temperature of a hot-rolled steel sheet according to the present invention uses a water-cooled surface heat transfer coefficient larger than that of a low-Si steel when the hot-rolled steel sheet is a high-Si steel. By predicting and calculating the winding temperature, the calculation accuracy is increased, and highly accurate winding temperature control is enabled.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of winding temperature control.

FIG. 2 is a graph showing a water-cooled surface heat transfer coefficient curve.

FIG. 3 is an explanatory diagram of a residual scale in a high Si steel.

FIG. 4 is a graph showing a difference in cooling rate between a low Si steel and a high Si steel.

FIG. 5 is a graph showing a difference in a water-cooled surface heat transfer coefficient curve between a low Si steel and a high Si steel.

FIG. 6 is an explanatory diagram of a run-out table cooling facility used in the embodiment.

FIG. 7 is a table showing a relationship between a calculated value and a measured value of a winding temperature.

[Description of Signs] 1 steel plate 2 finishing mill 3 run-out table 4,5 cooling header 6 coiler 7,8,10 thermometer

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yukihiko Yaida 3 Kashima-cho, Kashima-gun, Ibaraki 3rd, Kashima Works Sumitomo Metal Industries, Ltd. Kashima Works (56) References JP-A-59-229218 (JP, A) JP-A-6-218414 (JP, A) JP-A-6-256858 (JP, A) JP-A-6-262240 (JP, A) JP-B-60-35973 (JP, B2) JP-B-6-248 ( JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) B21B 45/02 320 B21B 37/00 BBM B21B 37/76

Claims (1)

(57) [Claims] When a hot-rolled steel sheet is water-cooled on a run-out table and wound, a winding temperature of the hot-rolled steel sheet is predicted and calculated using a water-cooled surface heat transfer coefficient, and the calculated value matches a target value. In the winding temperature control of the hot-rolled steel sheet for determining the water injection amount in the run-out table,
Winding of a hot-rolled steel sheet, wherein the water-cooled surface heat transfer coefficient is corrected so that the water-cooled surface heat transfer coefficient of the high Si steel is higher than the water-cooled surface heat transfer coefficient of the low Si steel in the region above ℃. Temperature control method.